The Volkswagen NILS commuter concept.

With the trend towards smaller cars spreading across the world, eccentric concept house Rinspeed has turned the movement on its head by unveiling the compact car that grows.

The Dock + Go concept, designed by Rinspeed founder Frank M. Rinderknecht, allows drivers to add a high-tech 'trailer' to the back of their vehicles which serves a variety of purposes.

Designed for the rapidly-growing number of tiny city cars on the road, where space is at a premium, the system is described as a 'backpack on wheels' for vehicles and can be adapted to handle whatever 'extension' is needed for the situation.

Demonstrating the dock with a Smart Fortwo model, for instance, Rinderknecht envisions an integrated heated box for pizza delivery drivers or a separate toolbox pack for workmen, to hDetatchable trunk can make your compact car biggerold what wouldn't fit in the vehicle.

In the biggest nod to the changing way we drive, Rinspeed says that the Dock + Go could also be used to hold a battery pack, providing extra range to electric vehicles when used on long trips -- an idea mooted last year by US-based Electric Motors and Vehicles Company with its 'Pru' generator trailer.

It may not offer a lot of storage space – but it certainly adds a ‘cool’ factor to the already cool Smart car.

The model is set to be unveiled at the Geneva Motor Show, which runs March 8-18, 2012 in Switzerland.